Intake air temperature estimation system for turbocharged engine

Abstract

An intake air temperature estimation system includes: an adiabatically compressed intake air temperature computing unit that computes an adiabatically compressed intake air temperature based on an intake air temperature before compression, an intake air pressure before compression and an intake air pressure after compression; and an estimated intake air temperature computing unit that computes an estimated intake air temperature. The estimated intake air temperature computing unit variably sets a coefficient of the function in response to an amount of change per unit time in the intake air pressure after compression such that a followability of the estimated intake air temperature to the adiabatically compressed intake air temperature at the time when the amount of change is large is higher than a followability of the estimated intake air temperature to the adiabatically compressed intake air temperature at the time when the amount of change is small.

What is claimed is: 
     
       1. An intake air temperature estimation system for a turbocharged engine, the turbocharged engine provided with a compressor being configured to compress intake air and supply the compressed intake air to a combustion chamber, the intake air temperature estimation system comprising
 an electronic control unit configured to 
 i) compute an adiabatically compressed intake air temperature based on an intake air temperature before compression, an intake air pressure before compression and an intake air pressure after compression, the intake air temperature before compression being a temperature of intake air before compression by the compressor, the intake air pressure before compression being a pressure of intake air before compression by the compressor, the intake air pressure after compression being a pressure of intake air after compression by the compressor, the adiabatically compressed intake air temperature being a temperature of intake air after compression by the compressor in an adiabatic state, 
 ii) compute an estimated intake air temperature with the use of a function that returns a first-order lag value with respect to the adiabatically compressed intake air temperature, the estimated intake air temperature being an estimated value of the intake air temperature after compression by the compressor, and 
 iii) variably set a coefficient of the function such that a followability of the estimated intake air temperature to the adiabatically compressed intake air temperature at the time when an amount of change per unit time in the intake air pressure after compression is large is higher than a followability of the estimated intake air temperature to the adiabatically compressed intake air temperature at the time when the amount of change per unit time in the intake air pressure after compression is small. 
 
     
     
       2. The intake air temperature estimation system according to  claim 1 , wherein
 the electronic control unit is configured to, when the coefficient changes with a reduction in an amount of change per unit time in the intake air pressure after compression, compute the estimated intake air temperature while executing a guard process, the guard process being a process of limiting an amount of change per unit time in the coefficient to a prescribed guard value or below. 
 
     
     
       3. The intake air temperature estimation system according to  claim 2 , wherein
 the electronic control unit is configured to execute the guard process such that the guard value at the time when the amount of change per unit time in the intake air pressure after compression is large is smaller than the guard value at the time when the amount of change per unit time in the intake air pressure after compression is small. 
 
     
     
       4. The intake air temperature estimation system according to  claim 2 , wherein
 the electronic control unit is configured not to execute the guard process when the adiabatically compressed intake air temperature is rising, and the electronic control unit is configured to execute the guard process only when the adiabatically compressed intake air temperature is decreasing. 
 
     
     
       5. The intake air temperature estimation system according to  claim 1 , wherein
 the electronic control unit is configured to, when the amount of change per unit time in the intake air pressure after compression is larger than or equal to a prescribed value, variably set the coefficient in response to the amount of change per unit time in the intake air pressure after compression. 
 
     
     
       6. The intake air temperature estimation system according to  claim 1 , wherein
 the electronic control unit is configured to compute the estimated intake air temperature by updating the estimated intake air temperature such that a relationship expressed by the following mathematical expression is satisfied, 
 
       
         
           
             
               
                 T 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   1 
                   ⁡ 
                   
                     [ 
                     new 
                     ] 
                   
                 
               
               = 
               
                 
                   T 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     1 
                     ⁡ 
                     
                       [ 
                       old 
                       ] 
                     
                   
                 
                 + 
                 
                   
                     
                       T 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                       ⁢ 
                       m 
                     
                     + 
                     
                       T 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         1 
                         ⁡ 
                         
                           [ 
                           old 
                           ] 
                         
                       
                     
                   
                   K 
                 
               
             
           
         
         where T 1   m  is the adiabatically compressed intake air temperature computed by the electronic control unit, T 1 [old] is the estimated intake air temperature before being updated, T 1 [new] is the estimated intake air temperature after being updated, and K is a coefficient that takes a value larger than or equal to 1.